In recent years, asphalt paving oil mixed with recycled rubber has emerged as a preferred paving material because of its superior physical properties and its potential as a solution to a major environmental problem: the disposal of scrap automobile and truck tires. A popular process for the use of such material is described in U.S. Pat. No. 3,891,585 and U.S. Pat. No. 4,069,182, both issued to Charles H. McDonald, the specifications of which are hereby incorporated by reference. According to a current form of this process, recycled crumb rubber obtained from scrap automobile tires is mixed with paving grade liquid asphalt (usually AR 4000) at a temperature of approximately 400 degrees F (199 degrees C.) to form a jellied composition of "asphalt-rubber" which is sprayed at 385-400 degrees F. (189-199 degrees C.) in quantities of approximately 0.55-0.65 gallons per square yard (2.5-2.9 liters per square meter) of pavement or used as a binder in hot mix asphalt (HMA).
A thick cloud of visible emissions is released into the air when hot asphalt-rubber is sprayed onto a pavement surface. These emissions result from the hot liquid coming into contact with the surrounding air and then contacting the pavement itself, both of which are much cooler than the liquid. The emissions produced in applying asphalt-rubber are much greater than those produced by spraying most other materials because non-rubberized materials are typically applied in smaller quantities and/or at lower temperatures. In contrast to asphalt-rubber, a tack coat of conventional paving grade oil is applied in quantities of only approximately 0.05-0.10 gallons per square yard (0.2-0.4 liters per square meter), and conventional prime coat oil is applied at temperatures of only approximately 150-180 degrees F. (63-82 degrees C.).
Although emissions from the spraying of asphalt-rubber compositions have not been shown to be harmful medically, they do present an "opacity" problem at the point of application due to more stringent air quality regulations adopted in recent years. This was investigated by Roberts Environmental Services of West Covina, California and is discussed in a document entitled "The Asphalt-Rubber Producers Group Ambient Air Sampling program" (June 1989), Which reports opacity readings of up to 90% at locations downwind of mobile asphalt-rubber operations.
Prior efforts to reduce emissions in the asphalt industry have focussed on devices for collecting emissions from substantially stationary sources, such as delivery trucks as they are being filled with hot mix asphalt (HMA), or on complex machines which mill, rejuvenate and reapply asphalt pavement in a slow, relatively enclosed process known as asphalt heater scarification/recycling. These systems have not been proposed for mobile spraying operations, however, and are not suitable for liquid asphalt-rubber applications.
Therefore, it is desirable in many instances to reduce or eliminate emissions from a mobile asphalt-rubber application process.